cleaning knives, more comments

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From:Gayle Callis <>
Date:Wed, 07 Apr 1999 13:40:32 -0600

I have found this discussion interesting.  I wonder what the vendors have
to say about this?  Also, if they give the advice, is it because they
have direct experience with "knife cleaning" and daily sectioning, or is
this blanket concrete evidence advice?  

I find comments about a knife being too sharp, you have to dull it an
interesting comment.  I have never found a knife too sharp for my
tastes/usage.  I section routinely at 2 um, with an "unclean" blade, 
without any problems (Accuedge, high profile, and have used the low and
a whole array of vendor manufactured blades.  Also, if you clean knives for
paraffin sections and not frozens, why?  If oil is the problem, would there
be a difference?  And if it is a sharpness problem why would you need
duller blades for paraffin vs the frozens? 

I always felt (what is often construed as too sharp a blade??) that the
differences in knife angles, even between lots of knives, was more of 
a difference, rather than a knife that is too sharp.  If I have problems
cutting a block, with a brand new knife, it often is a slight tweak of the
holder to fine adjust that takes care of the problem.  Other factors are
paraffin, tissue, and how it was processed.  I also found that a section
not forming correctly on a new blade was also linked to a truly square
edge on the block (un- bless those rounded corners on embedding molds!,
love the peel away molds, square corners!)  I often reshape rounded 
corners, and all goes well on a brand unclean blade.

so if cleaning is of prime importance, it would be to remove oil, and
the sharper the blade, the better I like it.  After all, I don't dull my
glass knives before use, and like my disposables to approximate these
blades as much as possible.  I did go through a time of cleaning disposables,
but overall found it didn't make any difference, and actually preferred the
"unclean"  Could that have been damage to the coating of the edge, teflon,
and whatever else has been used?  That is a good point.  

I have seen blades with too much oil gunk, wondered about those, but
never have had a section fall off from oil contamination of slide, 
Dirty slides - yes or mungey fingerprints on slide surface - sections didn't
like oily skin.  One study required NO fat carryover from slide to slide, and
that did require cleaning a knife between blocks, and everything else in the
vicinity of blade inside a cryostat.  

Sorry for the tirade, but have found this whole discussion educational,
At the risk of being a very "dull" person, I remain in the "unclean" camp!

Gayle Callis


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